Paper incorporating a wide elongate impermeable element, and a method of making of the same

ABSTRACT

This invention is directed to improvements in paper incorporating a wide elongate impermeable element, to a method of making such paper and to documents made therefrom. The method comprises the steps of first bringing an elongate, flexible, impermeable element into contact with a support surface prior to their entry into a vat of aqueous paper stock, then depositing fibres onto the support surface to form paper. The element has a width of at least 6 mm and the deposition of fibres is carried out in such a manner that as fibres are deposited on the support surface the elongate element is incorporated in the paper with regions of the element at least partially exposed at least one surface of the paper at least two sets of windows at spaced locations. The at least two sets of windows are formed by two sets of portions which are raised from the support surface relative to adjacent areas of the support surface. A first set of raised portions has a width transverse to a machine direction in which the paper travels during manufacture, which width is narrower than the width of the elongate element, and the second set of raised portions has a width transverse to a machine direction in which the paper travels during manufacture, which width is at least equal to the width of the elongate element. Thus during manufacture of the paper the elongate element is brought into contact with both sets of raised portions with edges of the elongate element being supported by the second set of raised portions.

This invention is directed to improvements in paper incorporating a wideelongate impermeable element, to a method of making such paper and todocuments made therefrom.

It is generally known to include elongate security elements in securitypaper, as a security feature. Such elements can be threads, strips orribbons of, for example, plastics film, metal foil, metallised plastic,metal wire. These security elements are included in the thickness ofsecurity paper to render imitation of documents produced from the papermore difficult. These elements help in the verification of securitydocuments as they render the view of the documents in reflected lightdifferent from that in transmitted light. To increase the securityprovided by the inclusion of such an elongate element, it is also knownto endow the element itself with one or more verifiable properties overand above its presence or absence. Such additional properties includemagnetic properties, electrical conductivities, the ability to absorbx-rays and fluorescence.

As a further security feature, it has been found to be particularlyadvantageous to provide windows in one side of the surface of the paper,which expose such elongate elements at spaced locations. Examples ofmethods of manufacturing such paper incorporating security elements withor without windows are described below. It should be noted thatreferences to “windowed thread paper” include windowed paperincorporating any elongate security element.

EP-A-0059056 describes a method of manufacture of windowed thread paperon a cylinder mould paper-making machine. The technique involvesembossing the cylinder mould cover and bringing an impermeable elongatesecurity element into contact with the raised regions of an embossedmould cover, prior to the contact entry point into a vat of aqueousstock. Where the impermeable security element makes intimate contactwith the raised regions of the embossing, no fibre deposition can occur.After the paper is fully formed and couched from the cylinder mouldcover, the contact points are present as exposed regions whichultimately form windows, visible in reflected light, on one side of abanknote paper.

WO-A-93/08327 describes a method of manufacturing windowed thread paperon a Fourdrinier paper-making machine. A rotating embedment means, witha modified profile for embossing, is used to drive an impermeableelongate security element into draining paper stock, on a Fourdrinierwire. The profile of the embedment means is such that raised portionsare provided which remain in contact with the security element duringthe embedment process. Thus, paper fibres are prevented from collectingbetween the security element and embedment means, such that the securityelement is subsequently exposed in windowed regions of paper.

For production reasons, in current manufacturing procedures the securityelement used in windowed or non-windowed paper is preferably oscillatedwithin the paper substrate by a small amount, for example, plus or minus6 mm from either side of a centre line. This is primarily to assistcutting and guillotining across the thread tracks of stacks of 500sheets. If the thread was not oscillated, the guillotine blade would bepresented with a very sharply defined area, of say 1 to 2 mm wide, ofpolymer/metal/paper built up from 500 sheets. This tends to blunt oreven chip the cutting blade. By oscillating the thread, this area isdistributed over a wider area of 10 to 15 mm, easing the passage of theblade through the 500 sheet stack. The result of thread oscillation isthat only parallel bars can be used in the design of the windows, if thebanknotes made from the paper are all to look the same.

Recent investigations have shown that impermeable threads of 4 mm to 6mm maximum width can be included in paper using the above methods ofpaper-making. This is due to the requirement for paper stock to flowaround the thread and form complete paper areas on the front of thethread in the finished document.

In Canadian patent specification CA-A-2,122,528, there is described ananti-falsification paper which incorporates a wide impermeable securitystrip with a width between 2 mm and 4 mm. The paper is of multiplydesign, with at least two paper layers produced on separate papermachines. The security strip is embedded in a first ply and hasperforations along the edges which permit water drainage and hence paperfibre deposition along the edges of the thread. The front of the stripis laid down over raised areas on the embossed cylinder mould coverbefore the raised areas enter the vat of paper stock so as to createwindows of exposed strip in the contact regions. The width of the raisedareas is narrower than the strip width to permit permeation through theperforations of the strip by paper fibres. However, the width of thestrip is so great that the paper formed on the back of the paper hasflaws in the form of arbitrary holes in the region of the strip. Asecond ply of ordinary paper is independently formed and the two arelaminated together and further processed, the second ply therebycovering the flaws in the back of the first ply and providing at leastone homogenous paper surface. In another embodiment, a third ply islaminated over the front of the first ply to wholly embed the securitystrip. In yet another embodiment, the width of the strip is selected tobe so wide that no paper forms on the back of the first paper ply toprovide a continuous exposed area on the back. The front of the strip islaid on a continuous raised area on the mould cover before the raisedareas enter the vat of paper stock to provide a continuous exposed areaon the front. A second ply of paper is then laminated to the first plyto form the finished security paper and give a homogenous paper layer onone side and a continuous exposed strip on the other.

In all of the prior art methods described above, the width of theelongate element which can be used is very limited. Furthermore, theareas of the threads which are exposed are restricted in terms of shape,due to the limitation imposed by the required embossings, and in termsof the areas, due to the nature of the paper-making technique itself.

WO00/39391 describes a method of making single ply paper which can havea wide strip at least partially embedded therein. This is achieved byblinding one or more selected areas of a porous support surface,depositing a first layer of paper fibres onto the porous support surfacearound the blinded areas, bringing an impermeable strip to lie incontact with the blinded areas of the support surface such that at leastthe edges of the strip overlie the deposited layer, and depositing afurther layer of paper fibres over the first layer and the impermeablestrip to securely embed the edges of the strip within the paper. Theblinded areas are impermeable, which substantially prevents thedeposition of fibres thereon before the strip is laid thereover. Thus,substantially no paper fibres are deposited on one side of the strip ina central region between edges of the strip to thereby expose acontinuous area of the strip at a first surface of the paper.Additionally a plurality of discrete translucent or transparent windowsare formed in a second surface of the paper in which the strip isexposed.

The preferred prior art production methods for windowed security paperrequire an embossed cylinder mould cover. The use of blinding is notgenerally used in paper-making techniques for the very reason that thepaper is preferred to be uniform and consistent. The appearance of holesand perforations is not a feature which is usually required.

As the impermeable strip contacts the support surface after some paperfibres have already been deposited round the blinded areas, it preventsany further fibre deposition over the blinded areas preserving thedesigns created in the blinding operation as clear areas. Whilst the useof embossed cylinder moulds covers restricts the width of securitythreads which can be embedded, with this method it is possible toproduce a document with any width of impermeable strip, from say 6 mm upto full document width, with paper “coatings” in any design, includingwatermarks, on the front side of the document. The back of the paper canbe made to contain a continuous exposed strip which can be used for thedisplay of indicia and the like.

However, it has been found that the windows formed by this method do nothave sharp, well defined edges, but tend to be non-uniform with paperfibres encroaching into the windows and partially obscuring them. Thepaper fibres are not long enough to bridge the impermeable material usedto blind the mould cover, but tend to mount up around the blindingmaterial. The motion of the cylinder mould rotating in the vat of stockcauses the fibre to be washed back into the hole, particularly along theleading edge.

In the method described in EP-A-0059056, however, whilst there is alimitation on the width of the security element which can beincorporated, the edges of the windows are well defined because theelongate security element makes contact with the raised regions of thecylinder mould cover before any paper fibres are deposited. Paper fibresare therefore able to enter the valleys between the raised regions sothat the security element is buried in the portions of the paper knownas bridges between the windows. However, it has been found that if wideelongate security elements are used in the method of EP-A-0059056, thenwindows are not formed when the width of the security element is widerthan the raised portions of the cylinder mould cover. The edges of thesecurity element sag over the edges of the raised regions and preventpaper fibres from entering the valleys between the raised regions, withthe consequence that the security element is continually exposed on themould cover side of the paper.

It is therefore an object of the present invention to provide animproved method of manufacturing paper incorporating a wide impermeablesecurity element with discrete transparent or translucent windows inwhich the windows have clearly defined edges and are uniformly formed.

The invention therefore provides a method of manufacturing papercomprising the steps of first bringing an elongate, flexible,impermeable element into contact with a support surface prior to theirentry into a vat of aqueous paper stock, said element having a width ofat least 6 mm, then depositing fibres onto the support surface to formpaper, the deposition of fibres being carried out in such a manner thatas fibres are deposited on the support surface the elongate element isincorporated in the paper with regions of the element at least partiallyexposed at at least one surface of the paper at at least two sets ofwindows at spaced locations, said at least two sets of windows beingformed by two sets of portions which are raised from the support surfacerelative to adjacent areas of the support surface, in which a first setof raised portions has a width transverse to a machine direction inwhich the paper travels during manufacture, which width is narrower thanthe width of the elongate element, and the second set of raised portionshas a width transverse to a machine direction in which the paper travelsduring manufacture, which width is at least equal to the width of theelongate element, such that during manufacture of the paper the elongateelement is brought into contact with both sets of raised portions withedges of the elongate element being supported by the second set ofraised portions.

The invention will now be described, by way of example only, withreference to the accompanying drawings in which:—

FIG. 1 is a cross-sectional side elevation of a schematic of apaper-making vat for use in the method and manufacturing of paperaccording to the present invention; and

FIGS. 2 to 5 are alternative arrangements of embossings and blindingsfor use on cylinder mould covers as shown in FIG. 1.

The method-of manufacturing paper according to the present invention isillustrated with reference to FIG. 1. A porous support surface, forexample in the form of a cylinder mould cover 10, is produced in a knownway. The mould cover 10 has raised portions formed by embossing, such asthose described in EP-A-0059056. The raised portions define the shape ofthe windows formed in the final paper. In this specification the term“window” includes a transparent or translucent region in the paper ofregular or irregular shape and occurrence.

In a known manner, the cylinder mould cover 10 is rotated in a vat ofpaper stock 11 as illustrated in FIG. 1. The paper stock may comprisefibres of natural materials, such as cotton, synthetic fibres or amixture of both. As it rotates, a wide flexible elongate impermeableelement 13, preferably having a width of at least 6 mm, is brought intocontact with the cylinder mould cover 10 above the level of the paperstock.

The raised portions 15, 16 are divided into two sets. A first set 15preferably provides a repeating pattern, the width of which is less thanthe width of the elongate element 13. A second set 16 is provided sothat at least parts or some elements thereof are located on either sideof the first set 15, the distance between the outer edges of said secondset 16 corresponds to at least the width of the elongate element 13. Thesecond set of raised portions 16 may comprise individual raised portionson either side of the first set 15, e.g. as shown in FIGS. 2, 4, 5 and6. Alternatively each or some of the raised portions of the second set16 may extend the full expected width of the element 13, i.e. having anoverall greater width than the first set of raised portions 15, as shownin FIG. 3. It should be noted that any reference to the width of thefirst or second set of raised portions 15, 16 refer to the widthmeasured transverse to the machine direction. The first set of raisedportions 15 define the shape of the main windows and are preferablylarger than those provided by the second set 16. Although smallersecondary windows will be provided by the second set of raised portions16, their main function is to support the edges of the wide elongateelement 13 during the manufacturing process and to allow paper fibres todeposit between the windows. Furthermore, the shape of the second set ofraised portions 16 can be designed so as to encourage the flow of paperfibres between the raised portions 15, 16, as described below. It ispreferable that the security element is not oscillated during themanufacture of the paper to ensure that the edges of the element 13 arein contact with and supported by the second set of raised portions 16.

This method has the advantage of allowing a greater range of designs forthe shape of the window than are possible if the entire raised area iswider than the security element 13, which would be limited to geometricshapes, such as rectangles.

Whilst it is preferred that the invention is made in a single ply ofpaper to form transparent or translucent windows, it is also possible tolaminate a second ply of paper to the back of the wide flexible elongateelement.

EXAMPLE 1

In the example shown in FIG. 2, the dolphins forming the first set ofraised portions 15 may be 12 mm wide, whilst the waves at the edges,forming the second set of raised portions 16, extend to 35 mm, i.e.considerably wider than the element 13, which is 18 mm wide. A series ofwindows is formed in the shape of dolphins when the element 13 is laidon the raised portions 15. The element 13, being impermeable, blinds themould cover in that region. The element 13 is supported on the waves,which are shaped to allow the flow of fibres between the raised portions15, 16, allowing paper to form in these regions. Windows are also formedby the waves where they are in contact with the element 13.

EXAMPLE 2

In the example shown in FIG. 3, the embossing of the dolphin is 12 mmwide and the wave supports are 18 mm wide. When an 18 mm wide element 13is run on the embossing a 12 mm wide window is formed in the shape ofthe dolphin and the waves are also exposed as windows where the element13 is in contact. The waves again are shaped to encourage the flow offibre into the regions between the dolphins.

EXAMPLE 3

The example shown in FIG. 4 is similar to that shown in FIG. 3 exceptthat the waves are positioned at the edges of the dolphin to provideindividual supports 18 mm apart, i.e. the width of the element 13. Againthe waves assist the flow of fibre to form paper between the raisedportions 15, 16.

EXAMPLE 4

In example 4 shown in FIG. 5 a window is formed in the shape of a largediamond which is 12 mm wide by 30 mm long. The smaller diamonds aboveand below provide support in the machine direction, to prevent surfacingof the element 13 between windows. The smaller diamonds at the sides arethe raised portions 16 for supporting the edges of the element 13 andallow the fibres to flow in underneath the element 13 and form paper inthe dark areas of the diagram. These will also appear as minor windowswhere the element 13 contacts them.

EXAMPLE 5

The example shown in FIG. 6 is similar to that shown in FIG. 5 exceptthat the large window 15 in the centre is formed in the shape of anellipse, which is 12 mm wide by 30 mm long. The smaller ellipses aboveand below provide support in the machine direction to prevent surfacingof the element between windows. The element 13 is 18 mm wide whilst thesmaller ellipses 16 which support the edges of the element have atransverse width of 22 mm, i.e. greater than the width of the substrate.Part of the ellipses 16 will appear as minor windows where the element13 contacts them.

This process therefore enables a wide strip of an impermeable element13, of a preferred width of at least 6 mm and preferably in the range of6 mm to 100 mm or wider, to be included in the paper. The width of theelement 13 could be very close to the width of a security document madefrom the paper, so that in finished documents just a narrow margin ofpaper runs down each edge of the document. (NB: although the element 13in such a context may not be narrow and elongate and thereforeappropriate to be described as a strip with respect to the finishedbanknote, it is a strip with respect to the full sheet of paper duringmanufacturing. Thus any reference in this specification to a “strip”should be interpreted accordingly). When viewed in reflection from thewire side, large transparent windows can be seen which are highlyvisible.

A wide strip of the impermeable element 13 may be used as a displaysurface for indicia, for example, de-metallised images, holographicimages, colour shifting areas, print or combinations of any or all ofthese which are highly visible in the large windows. However, if a plainclear element 13 is used, the windows will be partially translucent orwholly transparent. When viewed in transmission, from the wire side theindicia, the metallisation or colouring on the fully embedded edges ofthe element 13 also become visible. These edges may be provided withindicia which bleed from or complement any indicia contained on theexposed portion of the element 13.

One preferred material for the element 13 is BOPP of, say, 20micrometers thickness as this would help to maintain the “flatness” ofthe paper over the windowed region. However, other materials such as PE,PET or PK with other thicknesses may be used.

In one embodiment, de-metallised images are used which have large areasof transparent regions to provide a greater contrast within the windowsbetween the metallised and non-metallised areas. When the sheet isviewed from the “wire side”, the visibility of the bridges between thewindows is enhanced by its contrast to the metallisation.

The element 13 can advantageously be used as an information carrierand/or can contain a wide variety of known security features. These mayinclude the following;

-   -   de-metallised designs, which may comprise areas of substantially        removed metal to take advantage of the transparency of the base        film and provide a large area of transparent window;    -   holographic designs, which could comprise areas of full metal        and half-tone screens to provide partial transparency and/or no        metal. Under certain viewing conditions, with no metal, a        holographic image is still visible;    -   front to back print registration, in which features are printed        which would clearly exhibit Moiré patterns from both front and        back if a counterfeit were attempted. Alternatively, such        patterns could be produced on a transparent film prior to        insertion of the element 13 into the paper as a security feature        itself. The exact reproduction of such patterns are very        difficult to mimic;    -   different coloured print showing on the front to the back. The        print may be on either side of the strip or both on the same        side, with one colour hidden by the other on one side but        showing through on the other side;    -   liquid crystal films, such as those described in WO-A-94/02329,        in which colour changes are visible when a molecular liquid        crystal material is coated onto a watermark. Due to the scatter        effect of the paper surface, a large percentage of the possible        colour intensity is lost. By using a fully transparent window, a        very vivid colour change is visible both in reflection and        transmission;    -   luminescent or magnetic materials;    -   embedded de-metallised regions. As the areas of the element 13        at each edge are completely embedded, these can contain a        de-metallised type image which would only become visible when        the document was viewed in transmission. This area may also        mimic a similar adjacent area which is visible in reflection and        transmission or the metallisation could bleed out to the        adjacent area;    -   security embossing of transparent film with a security design        (e.g. a treasury seal) created during the printing process.        These may be blind embossed to produce a tactile/visible feature        or could include printing inks to further enhance visibility;    -   contact measurements in which at least one side of the element        is available for contact along its entire length. Measurements        can include resistance measured on a current being passed        through the element; contact to microcircuitry embedded within        the element; contact to activate a material within the element,        e.g., PVDF electrochromic; conductive polymers;

With such a large area available, it is possible to combine manyfeatures together on a element 13.

In addition, the element 13 could be perforated with holes of variousshapes to provide novel features or possibly machine readability, e.g.via airstreams.

The paper described above can be cut and printed to make all forms ofdocuments, including security documents such as banknotes, cheques,travellers cheques, identity cards, passports, bonds etc.

1. A method of manufacturing paper comprising the steps of firstbringing an elongate; flexible, impermeable element (13) into contactwith a support surface (10) prior to their entry into a vat of aqueouspaper stock (11), said element (13) having a width of at least 6 mm,then depositing fibres onto the support surface (10) to form paper, thedeposition of fibres being carried out in such a manner that as fibresare deposited on the support surface (10), the elongate element (13) isincorporated in the paper with regions of the element (13) at leastpartially exposed at at least one surface of the paper at at least twosets of windows at spaced locations, said at least two sets of windowsbeing formed by two sets of portions (15,16) which are raised from thesupport surface relative to adjacent areas of the support surface, inwhich a first set of raised portions (15) has a width transverse to amachine direction in which the paper travels during manufacture, whichwidth is narrower than the width of the elongate element (13), and thesecond set of raised portions (16) has a width transverse to a machinedirection in which the paper travels during manufacture, which width isat least equal to the width of the elongate element (13), such thatduring manufacture of the paper the elongate element (13) is broughtinto contact with both sets of raised portions (15,16) with edges of theelongate element (13) being supported by the second set of raisedportions (18).
 2. A method of manufacturing paper as claimed in claim 1in which the surface area of each of the raised portions of the firstset (15) is greater than the surface area of each of the raised portionsof the second set (16).
 3. A method of manufacturing paper as claimed inclaim 1 in which the transverse width of each of the raised portions ofthe second set (16) is at least equal to the width of the elongateelement (13).
 4. A method of manufacturing paper as claimed in claim 1in which a first plurality of the raised portions of the second set (16)are provided on one side of the first set (15) of raised portions and asecond plurality are provided on the other side, such that thetransverse distance between outer edges of the two pluralities of raisedportions (15,16) is at least equal to the width of the elongate element(13).
 5. A method of manufacturing paper as claimed in claim 1 in whichthe raised portions are formed by embossings of the support surface(10).
 6. A method of manufacturing paper as claimed in claim 1 in whichthe raised portions (15,16) are formed by blinded regions of the supportsurface (10).
 7. A method of manufacturing paper as claimed in claim 1in which the raised portions (15,16) are formed by a combination ofembossings and blinded regions.
 8. A method of manufacturing paper asclaimed in claim 1 in which the support surface (10) is a cylinder mouldcover.
 9. A method of manufacturing paper as claimed in claim 1 furthercomprising the step of laminating a second ply of paper to cover theback of the elongate element (13)
 10. A sheet of paper made by themethod of claim
 1. 11. A sheet as claimed in claim 10 in which theelongate element (13) is a security element having one or more securityfeatures.
 12. A security document comprising or produced from a sheet asclaimed claim
 10. 13. A security document as claimed in claim 12 inwhich the width of the elongate element (13) is the same as the width ofthe document.